Throughout this discussion, the proponents of the position that copyright is transferred only in a final version really do not make any legal arguments as such, just an assertion of what they wish were the situation (I wish it were too). But here is a legal point—the U.S. copyright law makes the difficulty with this position pretty clearly in section 202 when it states the obvious principle that copyright is distinct from any particular material object that embodies the copyrighted work. So it is simply not true to say that version A has a copyright and version B has a different copyright.